A customized `offsetof` implement, in modern C++.

offsetof.cc

#include <stdio.h>
#define offsetof(s, m) reinterpret_cast<size_t>(&reinterpret_cast<const volatile char&>(\
                static_cast<s*>(nullptr)->m))

struct S {
    char c;
    double d;
    char cc;
};

int main(void) {
    printf("the first element is at offset %zu\n", offsetof(struct S, c));
    printf("the double is at offset %zu\n", offsetof(struct S, d));
    printf("the third element is at offset %zu\n", offsetof(struct S, cc));
}